Sandwich type plaster boards such as gypsum plaster boards are to an increasing degree used in the building of houses. These boards are usually attached by means of screws onto a portative sub-structure. Large-surface walls can be established by assembling a plurality of boards. The joints formed between the individual boards can be filled by means of a filler material. Preferably a tape-like fleece material is put onto the filled joints which is finally smoothened.
Since in gypsum plaster boards the outer layers thereof significantly contribute to the strength of these boards, it proved to be advantageous in view of a high-quality processing of these boards to cut these boards comparatively precisely when needed so that the outer cover layers extend in an undamaged condition to the precisely defined edge of the board.
Cutting said boards to size is usually made by using a saw or a knife. Using a saw, the board can be easily separated completely. The edges are, however, relatively rough and are possibly jagged. When using a knife a smooth cutting edge can be achieved at least on one side of the board. In order to obtain a straight cut the use of a guide rail is imperative. When making short cuts, this guide rail can usually be held by hand. When making longer cuts, it is convenient to fix the guide rail for instance by means of screw clamps. If, however the guide rail is not fully straight or the board bends under the guide rail when being cut, there is a risk that the board is cut inaccurately and the blade of the knife does not penetrate sufficiently deep into the board so that a clearly defined separation line is not attained.